Reformer For Firing Reverberatory Furnace And Method Of Operating Said Reformer

Abstract

A reformer for firing a reverberatory furnace comprising a reaction chamber with a device for incomplete combustion of the gaseous and liquid hydrocarbon fuel accompanied by the formation of soot which is supplied into the working space of the furnace for ensuring a high luminosity of the flame.

Parent Case Text

This is a divisional, of application Ser. No. 103,127, filed Dec. 31, 1970 and now abandoned.

Description

The present invention relates to the devices for firing reverberatory furnaces and more particularly it relates to the reformers for firing open-hearth furnaces and to the method of their operation involving preliminary preparation of the fuel in order to ensure a high luminosity of the flame in the furnace.

The present invention can be used most successfully in reverberatory furnaces and fire-chambers whose efficient operation requires an intensively radiating and highly luminous flame.

Known in the art are devices for firing reverberatory furnaces with gaseous fuel, for example, natural gas, wherein the gas is preliminarily reformed, i.e., incompletely burned which is accompanied by the formation of soot. Such a device disclosed in U.S. Pat. No. 3,345,054, and called reformer, has a fire-proof reaction chamber with a cylindrical internal surface in which natural gas is reformed under the conditions conductive to a maximum transformation of carbon contained in gas into soot. The hot soot-gas mixture obtained in the reformer is mixed with the non-reformed gas thus producing a fuel mixture. On being introduced into the furnace, this mixture, containing a required amount of soot, gives a cone of flame which is characterized by high luminosity and, in consequence, has a high degree of heat transfer by radiation to the product being heated. This flame possesses the requisite rigidity owing to a high velocity of the fuel stream delivered into the furnace.

For a maximum efficiency of the reforming process, the gaseous fuel is burned incompletely in the reformer in a rotary turbulent diffusion flame. For this purpose the gaseous fuel is fed into the reaction chamber in the form of an axial stream through a correspondingly set branch pipe of the burner device whereas the air is delivered through a branch pipe set tangentially to the cylindrical internal surface of the reaction chamber and installed in the front part of the reformer, on its side wall. This produces a rotary diffusion flame in the reformer reaction chamber, this flame allowing more than 20% of the carbon contained in the gaseous fuel to be transformed into soot. This is considerably more than can be obtained with other arrangements for incomplete combustion. The air consumption in this case is 0.35-0.45 of the stoichiometric consumption.

However, in such an arrangement said reformer cannot reform liquid hydrocarbons such as the fuel oil used habitually as a stand-by fuel or, in absence of natural gas, as the main fuel.

The fuel oil can also be used as an addition to the gaseous fuel for imparting the required luminosity to the flame, and is fed directly into the working space of the furnace.

Under these conditions the fuel oil is delivered through spray nozzles or injectors. In contrast to the gaseous fuel this leads to the necessity of increasing the coefficient of surplus air and to unproductive utiliyation of a part of the furnace working space to prepare the fuel oil for burning. Besides, the soot yield in this case is not higher than 10 percent of the carbon contained in the fuel oil. This results in a higher consumption of fuel per ton of the product.

An object of the present invention resides in eliminating the aforesaid disadvantages.

The main object of the invention consists in providing a reformer with such a reaction chamber which would make it possible to use efficiently both the gaseous and liquid fuel and to produce a highly luminous flame.

According to the invention, this object is accomplished by providing the reformer chamber with a device for incomplete combustion of liquid hydrocarbon fuel, said device being installed near the device for incomplete combustion of the gaseous fuel and provided with a spray nozzle for supplying liquid fuel into the chamber. Such a universal burner device allows reforming both types of fuel and producing soot in the amount sufficient for the high luminosity of the flame.

As compared with the known methods of compound firing of furnaces with gas and fuel oil, preliminary reforming of fuel oil makes it possible to transform into soot up to 30 percent of the carbon contained in fuel oil and to produce a highly luminous flame which requires a smaller amount of surplus air owing to preliminary preparation of the fuel for combustion, thus reducing the consumption of fuel.

It is practicable that the liquid fuel should be supplied through an air atomizer spray nozzle which would be mounted coaxially inside the branch pipe supplying gaseous fuel in the burner device for firing gaseous fuel and, simultaneously, coaxially with relation to the reaction chamber. As it has already been stated above, the air required for incomplete combustion is delivered tangentially to the cylindrical internal surface of the reaction chamber through a specially set branch pipe. This ensures the optimum conditions for the maximum transformation of the carbon contained in the fuel into soot, avoiding at the same time the settling of carbon on the walls of the reaction chamber which interferes with its normal functioning. Besides, this arrangement of the burner device for liquid fuel ensures its easy installation, removal and replacement, when necessary.

It is practicable that the branch pipe supplying gaseous fuel in the device for burning this fuel should have a diameter equalling to 0.1 - 0.4 of the diameter of the reformer reaction chamber. This ensures a rational relation between the velocities of the streams of air and gaseous fuel and a maximum soot yield. Besides, this makes it possible to install the liquid fuel spray nozzle coaxially as it has been described above, without interfering with the conditions required for independent operation of the reformer on gaseous fuel.

In the preferable embodiment of the reformer reaction chamber, according to the invention, it is practicable that the reformer should incorporate some known devices for independent control of the flow rate of air, gaseous fuel, liquid fuel and of the agent which atomizes liquid fuel. This agent may be gas, e.g., natural gas, or air supplied under the required pressure. The independent supply of the above-mentioned substances allows the operator at the control desk to shift the reformer to operation on gaseous or liquid fuel or on their mixture with the required consumption ratio of these fuels.

According to the invention, if the furnace is fired with liquid fuel, the latter is gasified before burning in the reaction chamber by incomplete combustion accompanied by the formation of soot.

If gaseous fuel is not available, air is used for atomizing liquid fuel; besides, air can be used for complete combustion of a part of the liquid fuel outside the reaction chamber in the tunnel burners, from which the products of complete combustion are delivered tangentially to the internal surface of the reaction chamber. For better aerodynamics of the streams in the reaction chamber it is practicable to install an even number of tunnel burners, for example two burners opposed diametrically to each other.

A substantial advantage of the present invention lies in reaching a 10 percent economy of fuel as compared with the known methods of compound firing of furnaces with natural gas and fuel oil.

Described below is a preferable embodiment of the reformer according to the invention with reference to the accompanying drawing (which is a schematic longitudinal section through a part of an open-hearth furnace, including its firing throat, and one of the reformers communicating with said throat and furnace.

Installed in the firing throat 1 of the furnace 2 is a fire-proof nozzle 3 of a known design, communicating through a refractory channel 4 with the reaction chamber 5 of the reformer 6. The nozzle 3 is inclined to the horizontal to suit the required conditions of product heating in the furnace. The area through the channel in the nozzle 3 is selected so as to ensure the required velocity of the fuel mixture flow and to produce a rigid flame. The nozzle 3 is fitted with a branch pipe 7 for introducing the non-reformed part of gaseous fuel into the reformed products flowing through the nozzle.

The reaction chamber 5 of the reformer 6 accommodates devices for incomplete combustion of gaseous and liquid fuel. The burner device for gaseous fuel, e.g., natural gas, consists of a gas supply branch pipe 8 and an air supply branch pipe 9. The branch pipe 8 is installed coaxially with the reaction chamber 5 while the branch pipe 9 is set tangentially to the internal cylindrical surface of the chamber 5. The burner device for liquid fuel, e.g., fuel oil, comprises an air atomizer spray nozzle 10 of a known design provided with a pipe 11 for the delivery of the atomizing agent, as well as the above-mentioned branch pipe 9, a by-pass line 12 with a shutoff means 13 and a tunnel burner 14 of a known design, adapted for complete combustion of fuel. The fuel may be fuel oil, natural gas, coke gas or some other cheap fuel.

The spray nozzle 10 and the pipe 11 are set coaxially inside the branch pipe 8.

Part of the non-reformed gaseous fuel is supplied to the branch pipe 7 through the pipeline 15. The air is supplied to the branch pipe 9 through the pipeline 16 and the by-pass line 12. During operation of the tunnel burners 14 they are fed with fuel through the pipeline 17 whereas air is delivered through the pipeline 16. Part of the gaseous fuel being reformed is delivered to the branch pipe 8 through the pipeline 18. The reformed liquid fuel is delivered to the spray nozzle 10 through the pipeline 19. If the fuel is atomized by natural gas, the latter is supplied to the branch pipe 11 through the pipeline 20; if the fuel is atomized by air, the latter is supplied through the pipeline 21.

The pipelines 12, 15, 16, 17, 18, 19, 20 and 21 are fitted with shut-off means (gate valves), 13, 22, 23, 24, 25, 28, 26 and 27, respectively.

These means are provided with remote control included into the atuomatic system (not shown) of controlling the furnace firing and shifting this firing from one side of the furnace to the other.

If the open-hearth furnace is fired with gaseous fuel, e.g. natural gas, the shut-off means 23, 24, 26, 27 and 28 must be closed while the shut-off means 22, 13 and 25 must be open for admitting the required quantities of gas and air. It is recommended to reform and supply through the pipeline 18 about 40% of the entire amount of natural gas used for firing the furnace and to use about 4 m.sup.3 of air per 1 m.sup.3 of natural gas for incomplete combustion in the reaction chamber. At this air-gas consumption ratio, when gas is supplied in an axial stream through the branch pipe 8 while air is supplied in a tangential stream through the branch pipe 9 the soot yield reaches a maximum. It is practicable that the diameter of the branch pipe 8 should be 0.1-0.4 of the inside diameter of the chamber 5.

The hot soot-gas mixture produced in the chamber 5 flows through the channel 4 into the nozzle 3 where it is mixed with the non-reformed part of cold gas supplied through the branch pipe 7. As the non-reformed gas is thus heated, the fuel mixture delivered into the furnace 2 form the nozzle 3 is better prepared for complete combustion; as a result, said combustion is accelerated and proceeds at higher temperatures. All this increases the radiation heat transfer of the flame.

When the furnace is fired simultaneously with gaseous and liquid fuels there may be different combinations of the flow rates of these fuels. In one of the methods it is recommended to reform such a quantity of fuel oil which corresponds to 20 percent of the total heat spent for firing the furnace. In this case it is necessary to open correspondingly the shutoff means 13, 22, 27 and 28 to supply air for reforming the fuel oil through the by-pass line 12; the natural gas is fed through pipeline 15 and branch pipe 7 into the reformed products flowing through the nozzle 3; the natural gas is also supplied through the pipeline 21 for atomizing the fuel oil delivered through the pipeline 19.

It is also possible to use other combinations of the consumption ratio of the gaseous and liquid fuels delivered into the reaction chamber 5 for the preparation of the hot soot-gas mixture and into the nozzle 3 for mixing cold gas with said mixture.

Though natural gas can be delivered for reforming into the reaction chamber 5 simultaneously with fuel oil, it is preferable to employ such a layout where the fuel oil used for furnace firing is preliminarily reformed and gasified so that the furnace is supplied through the nozzle 3 with the products of reforming mixed with natural gas. Thus, the furnace receives a spray of a fuel mixture consisting wholly of heated gases containing soot. Subsequent flame firing of this gaseous fuel mixture proceeds with low surplus air coefficients characteristic only of the gaseous fuel and, correspondingly, at high temperatures. This ensures a high luminosity of the flame and a high heat transfer by radiation.

When natural gas is not available and the furnace is fired with fuel oil, it is necessary to close the shut-off means 22, 25, 27 and open the shut-off means 26 and 28 for delivering, respectively, air as an atomizing agent, and liquid fuel for reforming. The process of reforming can in this case proceed owing to the heat produced by the combustion of the part of fuel oil delivered into the chamber 5 through the spray nozzle 10. The air is then delivered for reforming through the by-pass line 12 and the shut-off means 13.

The reforming process can also proceed owing to the heat produced by the combustion of a part of fuel oil in the tunnel burners 14. It is preferable to have an even number of tunnel burners 14 and arrange them diametrically opposite to each other for better aerodynamics of the streams in the chamber 5. In this case said burners are supplied with the corresponding amounts of fuel oil and with the quantity of air sufficient for complete combustion of fuel oil. For this purpose the shut-off means 23 and 24 are opened through a required angle and the shut-off menas 13 are closed. The total recommended ratio of the consumption of air and fuel oil delivered into the reaction chamber is 3 m.sup.3 /kg. This amount includes the air spent for the atomization of fuel oil. These conditions ensure the reforming time necessary for obtaining the sufficient yield of soot as well as the preliminary gasification of liquid fuel before burning it in the furnace. As a result, the fuel mixture delivered for flame burning contains combustible hot gases and a sufficient proportion of soot. Owing to this the flame combustion proceeds with low coefficients of surplus air which are characteristic only of gaseous fuel, and at high temperatures. This also ensures a maximum radiation of the soot contained in the flame.

While using liquid hydrocarbons as fuel, the invention makes it possible to subject them to preliminary gasification and transform them simultaneously into soot in the quantities required for high luminosity of the flame. The high temperatures produced by the burning of such prepared fuel increase the radiation of the soot in the flame and of the flame as a whole which intensifies the heat transfer and gives at least a 10 percent saving in fuel.

Claims

What we claim is:

1. A reformer for firing a reverberatory furnace comprising: a reaction chamber with a cylindrical internal surface communicating with the working space of said furnace and intended for incomplete combustion in it of the hydrocarbon fuel, said combustion being accompanied by the formation of soot to be delivered into the furnace; a device for incomplete combustion of gaseous hydrocarbon fuel located in said reaction chamber; said device provided with a branch pipe supplying gaseous fuel into said chamber and installed coaxially with the latter, and a branch pipe supplying air into the same chamber, located tangentially to the internal surface of said chamber; and a device for incomplete combustion of liquid hydrocarbon fuel, installed in said chamber near said device for incomplete combustion of gaseous fuel and provided with a spray nozzle for the supply of liquid fuel into said reaction chamber.

2. A reformer according to claim 1 wherein there is an air atomizer spray nozzle for the supply of liquid fuel, located coaxially inside said branch pipe for the supply of gaseous fuel.

3. A reformer according to claim 1 wherein the diameter of said branch pipe for the supply of gaseous fuel into said reaction chamber is 0.1-0.4 of the inside diameter of this chamber.

4. A reformer according to claim 1 wherein said devices for incomplete combustion of gaseous and liquid fuels are provided with known means of independent control of the flow rate of the air, gaseous and liquid fuels, and of the agent used for atomizing the liquid fuel.